Implantable medical devices are used to deliver neuromodulation therapy to patients to treat a variety of symptoms or conditions such as chronic pain, tremor, Parkinson's disease, epilepsy, incontinence, or gastroparesis. Neuromodulation may involve delivery of neurostimulation therapy, in the form of electrical pulses, via one or more leads that include electrodes located proximate to the brain, spinal cord, peripheral nerves, skin, neuronal ganglia, or nerves to organs. Neuromodulation may also involve use of an implantable drug delivery device, to chronically deliver metered dosages of a drug to target regions in the body via a catheter. Neuromodulation may involve the simultaneous use of both modalities, i.e., neurostimulation and drug delivery, for optimal efficacy.
Prior to implantation of a neuromodulation device, the patient may engage in a trial neuromodulation period, in which the patient receives an implanted or external trial neuromodulation device on a temporary basis. An external trial neurostimulator screener, for example, may be coupled to an implanted lead via a percutaneous lead extension. In either case, the trial neuromodulation permits a clinician to observe neuromodulation efficacy and determine whether implantation of a chronic neuromodulation device is advisable.
The trial neuromodulation period also may assist the clinician in selecting values for a number of programmable parameters in order to define the neuromodulation therapy to be delivered to a patient. For example, for a neurostimulation, the clinician may select an amplitude, which may be current- or voltage-controlled, and pulse width for a stimulation waveform to be delivered to the patient, as well as a rate at which the pulses are to be delivered to the patient. In addition, the clinician also selects particular electrodes within an electrode set on a lead to be used to deliver the pulses, and the polarities of the selected electrodes. With drug delivery, the clinician may select dosing and concentration of the drug in the device, and timing intervals also.
The results of the trial neuromodulation process can be inconsistent. For example, the trial neuromodulation process may be hampered by subjective and possibly inconsistent feedback from the patient concerning observed efficacy. In addition, the trial neuromodulation process may yield information that is indicative of short-term, diagnostic efficacy, but less indicative of long-term, prognostic success.